AOX – Adsorbable organically bound halogens

The chemical-analytical parameter AOX, short for adsorbable organically bound halogens, is an important characteristic in industrial and environmental analytics. It provides information about the presence and the concentration of organic halogen compounds such as chlorine, bromine and iodine in a sample.

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Combustion ion chromatography to analyse for AOX

What is AOX?

UAOX is a sum parameter used in chemical analytics primarily for the assessment of water and sewage sludge. Since 1985, it has been a standard parameter in the list of German standard methods for the examination of water, waste water and sludge.

The method for determining AOX is specified worldwide in numerous standards. Along with the ASTM and EPA standards, the international standard ISO EN 9652 is most frequently used to determine AOX. Here the sum of the adsorption of halogen compounds on activated carbon is determined.

What is a sum parameter?

A sum parameter provides a summary of one or more substance groups under specific analytical conditions but does not provide information about the individual substances (also termed individual parameters). Other crucial sum parameters in the context of the determination of the overall levels of halogens are: AOF and EOX.

The sum parameter AOX

This parameter is of crucial importance because it provides insights into the contamination of the environment with halogenated organic compounds. These compounds are potentially toxic and can have long-term effects on ecosystems and human health. The analytical determination of AOX helps with the monitoring of the presence and concentration of these compounds, which is imperative for compliance with environmental standards and the evaluation of clean-up measures. By acquiring this specific group of chemicals, AOX analysis assists environmental authorities, industrial organisations and research institutes to better understand and manage the effects of anthropogenic activities on the natural environment.

The characteristics of adsorbable organically bound halogens

Organically bound halogens are chemical compounds that contain one or more halogen atoms such as chlorine, bromine, iodine or fluorine in organic molecules. These halogen atoms are bound to organic carbon chains producing a large number of compounds used in various industries.

The chemical structure of organically bound halogens gives them a series of unique characteristics that can be both useful and potentially dangerous. Their persistence in the environment and their tendency to bioaccumulation can cause long-term environmental problems. Furthermore, some organic halogens can be toxic and have harmful effects on the health of humans and animals, in particular if they are present in high concentrations.

What is the difference between AOX and EOX?

The difference between AOX and EOX (extractable organically bound halogens) is fundamental in environmental analytics, because the two parameters acquire different aspects of the halogen load. AOX refers to the total halogenated organic compounds in a sample that can be adsorbed on activated carbon, which makes possible the direct estimation of the water-soluble contamination by halogens of relevance for the environment. This value is particularly informative for the assessment of the quality of water and waste water.

The sum parameter EOX

EOX, on the other hand, acquires those halogenated organic compounds that can be extracted from solid or semi-solid matrices using solvents and provides insights into the halogen load that can be mobilised potentially in soil, sediments or sludge. The clear distinction between the two parameters makes it possible to take a more differentiated view of the environmental impact and to identify specific sources and pathways of contamination, which is imperative for targeted quality assurance and environmental protection strategies.

Combustion ion chromatography to analyse for AOX

Quality Analysis analyses your sample for AOX

Irrespective of whether the issue is water, soil or other matrices – our experienced team uses advanced combustion ion chromatography (CIC) that meets the requirements of modern environmental analytics, quality control and statutory regulations. Quality Analysis analyses the halogen load in your samples as per the highest standards. At Quality Analysis we rely on the latest standards and methods for our AOX analysis to ensure that your samples are analysed with the highest precision and in accordance with internationally recognised standards. Our accredited test laboratory applies, among others, DIN EN ISO 38409-59, the authoritative standard for the determination of adsorbable organically bound halogens to guarantee you exact, dependable, results.

AOX: halogenated organic compounds, natural and man-made

The origin of halogenated organic compounds is a complex mix of natural and anthropogenic influences that requires comprehensive analysis and monitoring to understand and minimise potential environmental effects.

Natural sources of AOX through biological and geological processes
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Natural sources of organically bound halogens

Halogenated organic compounds are produced by biological processes involving microorganisms, algae and plants, among other means. An example is marine algae and some plants that synthesise bromine compounds as a protection measure against other organisms that consume them. Halogenated organic compounds can also be produced by geological processes such as the weathering of rock or the natural release of halogens from the Earth's mantle.

Anthropogenic sources of AOX e.g. through incineration
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Anthropogenic sources of organically bound halogens

Human activities also make a significant contribution to the release of halogenated organic compounds. Synthetic AOX compounds are known above all as harmful substances, for example DDT, dioxins, polychlorinated biphenyls (PCBs) or chlorofluorocarbons (CFCs). They can also enter bodies of water, waste water or the air directly as agricultural chemicals or as cleaning agents from industry or households. Moreover, halogenated organic compounds accumulate in the environment due to the disposal of industrial waste and domestic waste water, in particular if this waste is not treated correctly. The combustion of waste and fossil fuels also results in the release of halogenated organic compounds such as dioxins and polychlorinated biphenyls (PCBs).

Many everyday products contain AOX, e.g. electronic components, plastics and packaging materials

In which products is aox found?

Adsorbable organic halogen compounds (AOX) can occur in numerous products and materials that are widespread in everyday life. These materials and products include plastics, textiles, electronic devices, construction and insulation materials as well as packaging materials. They can contain halogenated additives that may be released during manufacture or use. For example, many plastics contain halogenated flame retardants, while textiles are often treated with halogenated chemicals to make them flame-retardant or water-repellent. Plastic housings and printed circuit boards for electronic devices, construction and insulation materials as well as packaging materials can also contain halogenated components.

The significance of AOX analysis: identification and monitoring of organic halogen compounds

AOX analysis plays a crucial role during the identification and monitoring of halogen compounds in various environmental matrices and products. By means of the determination of the quantity of adsorbable organic halogens, potential hazards for the environment and human health can be identified and evaluated. This analysis makes it possible to quantify the contamination of water, soil and various products with halogenated compounds and therefore monitor pollution as well as compliance with regulations.

Because halogenated organic compounds such as organic chlorine compounds have a negative impact on the human body and are potentially carcinogenic, AOX analysis is an important instrument for the evaluation and control of the quality of the environment and is used as the basis for the development of risk reduction measures.

Verification of freedom from halogens by means of aox analytics

The verification of freedom from halogens is a critical step in various sectors, in particular in areas such as electronics, construction and packaging. By means of AOX analytics, organisations can ensure that their products or materials are free of halogenated compounds that could be potentially harmful for the environment or health. This aspect is particularly important because some halogenated compounds such as brominated flame retardants or chlorinated paraffins are toxic and may be persistent.

Analysis of the sum parameter AOX using combustion IC

Combustion ion chromatography (CIC) for AOX analysis

Combustion ion chromatography (CIC) is an advanced method for the determination of adsorbable organically bound halogens (AOX) in environmental samples. Samples for the determination of organically bound halogens (AOCl, AOBr, AOI) must be acidified using nitric acid to a pH value of less than 2 before the adsorption step.

For the determination of AOX, a specific quantity of the sample is then placed in contact with activated carbon to obtain an accumulation of the halogen compounds. This step is crucial because it forms the basis for the efficient isolation of the relevant halogens.

Batch and column methods for sample preparation

Samples are generally prepared using either the batch method or the column method. The former is often the method of choice, however it is very laborious and requires the full attention of the user. The total time per sample is also not predictable, in particular if samples containing particles need to be analysed. Using the column method, it is possible to analyse straightforwardly even those samples that are rich in particles. This method offers varying degrees of automation and reduces handling steps and possible mistakes.

Combustion and Analysis

The next step is combustion. During this process, the temperature plays a crucial role: it must be high enough to ensure complete combustion of the organic compounds. During combustion, the halogens are converted into their ionic forms, which is an essential prerequisite for the subsequent ion chromatographic analysis. Ionisation permits the specific detection and quantification of the halides, as a result AOX values can be determined with high accuracy. By using ion chromatography as the detection method, it is possible to identify the previously organically bound halogens, chlorine, bromine and iodine (in the form of chloride, bromide, iodide) separately and also to acquire previously organically bound fluorine (AOF) at the same time.

The result of the analysis

The results of the AOX analysis are typically specified in micrograms per litre (µg/L) for aqueous samples or in micrograms per kilogram (µg/kg) for solid samples and sludge. These values represent the total concentration of adsorbable organically bound halogens in the sample. A high AOX value can be indicative of significant contamination of the sample with organic halogen compounds, which can affect the environment as well as the health.

Summary: AOX

The AOX parameter acquires the total amount of adsorbable organic halogens such as chlorine, bromine and iodine in environmental samples and is crucial for the assessment of the quality of water and soil. The analysis using a sum parameter assists with the monitoring of environmental pollution due to halogenated organic compounds and is imperative for environmental protection measures as well as quality control in various industries.

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